A conventional downcomer may be used in distillation, absorption, extraction and other fluid contacting operations along with a fluid-contacting device. As illustrated in U.S. Pat. No. 3,784,175, a downcomer aids in the mixing or separation of fluids. A downcomer typically comprises a vertically extending structure similar to pipes or ducts.
When used in a boiling water reactor (BWR), the downcomer is associated with a fluid-contacting device. The downcomer typically connects an upper portion of the fluid-contacting device with a lower portion. The downcomer, thus, serves as a passageway for descending fluids. Often, fluid mixing occurs in the downcomer. For example, hot reactor fluids may be mixed with cool feedwater. Consequently, it is important to maintain proper vertical alignment between the downcomer and the upper and lower portions of the fluid-contacting device and any other components associated with the downcomer.
In conventional BWR systems, existing jet pump downcomers are generally held in place by only a restraining ring. The downcomer is typically located in the restraining ring by two adjustable screws and a wedge. Often the screws are tack welded in place. The wedge rides on a guide bolt, and is held in place mainly by gravity. The described arrangement can loosen under vibration, causing long and expensive fieldwork to eliminate gaps between the downcomer and the wedge and to readjust the screws.